Remote Backup from MyCloud to MyCloud Mirror No Longer Works

I have a MyCloud running Firmware 2.41.116 that I had been successfully backing up to a MyCloud Mirror that is now running 5.10.122. They are both connected to an Apple Airport Extreme wifi router. At one point the backup started to fail. It may be coincident with the Mirror’s upgrade to release 5 but I’m not sure.

I’ve gone through all the instructions I can find to create a new remote backup job but it keeps failing. When I get to the part where I select the Destination folder, the login to the Mirror fails (" * Invalid Remote Backup Password. Try again."). My searches for what to do next are a mangled nightmare of circular references all leading to “you’re f’ed.”

You are my last hope.

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